This invention relates to a pneumatic shuttle picking mechanism and in particular, to a pneumatic picking mechanism in which a piston is moved in a cylinder by pressurized fluid and a rod attached to the piston drives a weaving shuttle.
In mechanisms of this type, the flow of the pressurized fluid from a reservoir to the cylinder is controlled by a main valve having a valve seat, a valve member and a valve guide in which the valve member is slidably mounted. An auxiliary valve actuates the main valve by establishing a pressure differential between the front and rear sides of the valve member.
Such a pneumatic shuttle picking mechanism is disclosed in U.S. Pat. No. 2,677,933. In the mechanism of the '933 Patent, the reservoir annularly surrounds the cylinder, and the valve seat is formed by the open end of the cylinder into which the forward cylindrical end of the valve member can be pushed to close the main valve. The pressure prevailing in the cylinder, and the operating pressure prevailing in the reservoir surrounding the cylinder affects the front face of the valve member. The rear face of the valve member can be subjected to high pressure by way of the auxiliary valve, which causes closure of the main valve, or to atmospheric pressure, which causes opening of the main valve.
With the main valve open, the pressurized gas in the reservoir flows into the cylinder and moves the piston which drives the shuttle by way of the piston rod. With the main valve closed, there exists a connection from the cylinder cavity to the outside through a passage in the main valve. Gas present in the cylinder cavity can thus escape as the piston is urged into its starting position by the arriving shuttle. In this way, the pneumatic picking mechanism acts also to decelerating the shuttle.
In the mechanism of the '933 patent it is a disadvantage that a relatively large part of the energy accumulated in the reservoir by the pressurized gas is required for opening the main valve. It is a further disadvantage that the piston is returned to its starting position exclusively by the kinetic energy of the arriving shuttle. No means are provided to return the piston, and with it the shuttle, to its starting position, if the piston does not reach this position solely by the kinetic energy of the shuttle.
U.S. Pat. No. 3,698,444 describes a pneumatic picking mechanism in which the piston of the mechanism drives the picking arm by way of a crank mechanism. In this case, pressurized fluid is supplied from a reservoir to a cylinder under the control of a magnetically actuated main valve. The '444 mechanism, however, requires a significant investment in mechanical components owing to the crank mechanism.
U.S. Pat. No. 4,082,118 describes a further pneumatic picking mechanism in which the pressurized fluid is provided by a second cylinder whose piston is driven by the loom main shaft. With this arrangement, however, the pressure in the shuttle driving cylinder cannot be built up rapidly enough.
It is therefore an object of the present invention to provide a pneumatic shuttle picking mechanism in which the piston can be subjected to the full pressure prevailing in the reservoir without major losses and within a very short time, and which ensures that the piston returns to its starting position.